This invention relates to an apparatus for feeding grinding balls into a ball mill of a type such as a generally horizontal, cylindrical drum for pulverizing raw material. More particularly, the invention relates to an apparatus for uniformly feeding a few balls at a time into a ball mill.
It is well known to pulverize iron ore, limestone, cement, coal, phosphate, copper ore and the like in rotating drums containing steel or iron balls generally ranging in size from 1 to 5 inches (25-127 mm). The raw material is crushed between the balls resulting from the cascading action of the balls as the ball mill is rotating.
The metal balls gradually wear away from the continual rubbing and impact between each other. New balls eventually must be fed into the ball mill. To operate at peak grinding efficiency, it is desirable to uniformly feed new balls into the ball mill at approximately the same rate as old balls wear out. Depending on the type balls used for grinding a specific raw material, the ball attrition rate can be accurately determined.
Raw material is normally fed into ball mills at rates corresponding to the output of the pulverized material. The input rate of raw material is frequently controlled using such parameters relating to grinding efficiency as sound, power consumption, fineness of pulverized material, etc. Using the same parameters have been proposed in the prior art for controlling feed rates of grinding balls. However, devices for uniformly feeding a few balls at a time that can correspond to the ball attrition rate in a grinding mill are not known in the art. Although new balls may be systemically added to a grinding mill, they are generally added in batches of several hundred pounds at a time. This cyclical loading of the grinding mill greatly increases the power requirements to operate the grinding mill. More importantly, the grinding efficiency of the grinding mill is decreased. Peak grinding efficiency cannot be maintained if the ratio of balls to the ore to be pulverized is not uniformly maintained.
Known devices for feeding balls into grinding mills generally are large machines which are costly to operate, frequently become jammed with balls, and/or fail to uniformly feed a few balls at a time into grinding mills. U.S. Pat. No. 3,542,300 discloses a large ball hopper for feeding balls into a ball mill. The hopper includes a number of compartments for holding balls. The balls are periodically released by rotating the entire hopper, including its complete charge of balls.
Our improved ball feeding apparatus overcomes the problems described above by controllably feeding balls from a ball storage hopper into a small rotating discharge drum having ball compartments. The drum is operated at a predetermined speed to uniformly feed a few balls at a time into a grinding mill. As a ball charge is emptied from each compartment, the drum rotates an empty compartment into an in-line relationship with the ball storage hopper for refilling with a new charge of balls.